The differentiation of specific cell types in mammals is mediated by differential gene expression. To understand the regulation of the development and differentiation of a particular cell type, it is important to understand what differential gene expression occurs in that cell type and how this gene expression is regulated. This proposal seeks to understand the differentiation of spermatogenic cells by analyzing the differential expression of one example gene, phosphoglycerate kinase-2 (Pgk-2). The Pgk-2 gene is expressed only in spermatogenic cells and this specific expression is regulated primarily at the transcriptional level. The aims of this proposal are to define the components of the active Pgk-2 transcript ion complex as they occur in adult spermatogenic cells that express the Pgk-2 gene. These components will include protein transcription factors that bind to specific sequences in the regulatory region of the Pgk-2 gene, and specific chromatin states that must be achieved in the Pgk-2 gene in order for the transcriptional process to occur. The final experiments proposed in this application are designed to characterize the development of the active Pgk-2 transcription complex by examining earlier, non-expressing cell types in the spermatogenic lineage to determine when each component of the active complex becomes established. It is hoped that understanding of the components of the active Pgk-2 transcription complex and how they are put together will contribute to an understanding of how genes are regulated in spermatogenic cells and ultimately how cases of defective gene expression in spermatogenic cells might be treated.